1. Field of the Invention
The present invention relates generally to sensors for transaxles and, more particularly, to a drainage and pressure relief vent in a vehicle speed sensor for a transaxle of a motor vehicle.
2. Description of the Related Art
Sensors are typically used in a variety of applications, including motor vehicles. The environment in which the vehicular sensor may be subject to is also varied, and may involve temperature extremes, moisture, and fluids such as oils or fuels. The sensor may require protection from its environment in order to preserve its functionality.
Motor vehicles, including those having front wheel drive or four wheel drive transaxles, utilize an electromechanical speed sensor to provide vehicle speed information for a speedometer system of the vehicle. For a front wheel drive motor vehicle, the vehicle speed sensor is mounted in an extension housing of the transaxle (a transmission mounted across the axle), and for a four wheel drive motor vehicle, the vehicle speed sensor is mounted on a differential for the transaxle. The vehicle speed sensor is driven directly by a driveshaft of the transaxle, and generates a predetermined number of pulses per sensor shaft rotation. The vehicle speed sensor itself is protected by an external housing. There may be an empty space or cavity created between the vehicle speed sensor itself and the external housing. An example of a transaxle and vehicle speed sensor is disclosed in U.S. Pat. No. 4,875,391 to Leising et al., the disclosure of which is hereby incorporated by reference.
The transaxle contains hydraulic fluid to lubricate and protect its moving parts. It is possible for hydraulic fluid to enter the vehicle speed sensor through one or more possible locations: along a shaft bearing surface due to pumping or wicking action; along a lower external housing interface due to molding irregularities; and along an ultrasonic weld bonding an upper body portion to a lower body portion of the external housing. The hydraulic fluid that enters the vehicle speed sensor tends to accumulate in the cavities therein. This may result in several undesirable conditions: a fluid leak, fluid wicking into a connector or wiring harness of the vehicle speed sensor and connector sealing problems.